We have been studying the efficacy of local injections of botulinum toxin for the treatment of different types of focal dystonias. Botulinum toxin injected in small doses directly into muscle binds to the neuromuscular junction, and inactivates it for approximately three months. We have also used botulinum toxin to study the physiology of focal dystonias. Studies of the utility of botulinum toxin are being carried out in writer's cramp (and its varients such as pianist's cramp) in open~label and double~blind trials. Treatment appears effective at least in the short~ term. Longer follow~up on our patients showed that 49% of patients find botulinum toxin injections of persistent benefit. Patients who continued treatment were frequently women with nonlocalized symptoms or dystonic cramp, and a long duration of benefit. Five patients with arm tremor have been treated to date. One patient, with dystonia and essential tremor, has had an excellent response. Three patients have had partial benefit, and one patient has had no improvement. We are conducting a phase I trial of botulinum toxin type F to see if this will benefit patients who have developed antibodies to type A. It appears to have similar efficacy and side effects to type A, although the duration of action is slightly less.